A number of devices are available for measuring the distance between two points. Some of these have been adapted to work within a surgical wound. One of the most common measuring devices is a ruler. However, there are several problems with using a ruler to measure within a surgical wound. First, several size rulers are needed so that one is available that will fit within the wound. Often, the surgeon still has to cut the ruler to fit within the wound to obtain a measurement. Reading the measurement in the wound is often difficult because tissue, blood, and other fluids obscure the markings on the ruler. A ruler is difficult to use when measuring between two circumferential objects like spinal rods.
A three-sided ruler was designed to work better within the surgical site. Each side of the ruler measures a different distance, so that the ruler can be turned to obtain the most accurate distance. The reading must be done in the wound and the lighting is critical to make an accurate measurement. The same problems still exist with this modified ruler. Several sizes are needed to fit within the wound and measure the distance between sites. Accurate measurements are still difficult to read because the measurement is done in the wound with blood, tissue and other fluids in the way.
Another device used to measure between two points in surgery is the forceps or compass-type device. The device is inserted into the wound, one leg is directed at the first measuring point and the second leg is moved to the second point. The device is then removed from the wound and the distance between the two legs is measured against a ruler. This device requires an additional step and the measurement is less accurate because it is transferred to a ruler outside the wound. This device is also more expensive than the ruler.
U.S. Pat. No. 4,226,025 to Wheeler relates to a caliper for measuring the length, width, area and/or volume of living parts of mammals during surgery. The caliper includes a pair of long straight arms which are approximately parallel in a closed position and which pivot apart in a scissors movement in order to position the body part between the distal ends of each arm used for measuring. This device is useful for measuring cross-sectional areas or length of a line; however, it still is difficult to measure between two points such as spinal rods using this device because it has to be held in position against the object being measured and then compared to a measuring scale remote from the surgical site.
As noted above, prior art devices for measuring within a surgical site have either been not efficient or not very accurate. During a procedure the surgeon typically needs to measure the distance between two points to determine the appropriate size implant needed. An example use for this device is to aid the surgeon in determining the correct size cross-connector needed for additional stabilization of the spinal rods used for stabilizing adjacent vertebrae of the spine. There may be hooks or screws already placed on the rods which make placement of the cross-connector difficult. An accurate measurement of the distance between the two points on the rods to determine the size cross-connector is important to the surgeon and the patient as it can reduce the time of the surgery.
U.S. Pat. No. 3,738,355 (“Salvatore”) discloses a bone gage for measuring the diameter of a bone. The device comprises a tube having an opening from which extends a longitudinal hook means 28. The jaws 29A,B of the hook means 28 open when covering sheath 40 is moved proximally. Longitudinal hook means 28 can not be retracted into the body, and so does not have axial translation capability relative to the opening.
U.S. Pat. No. 4,450,834 (“Fischer”) also discloses a measuring device for measuring the diameter of a bone. The device comprises a tube having an opening from which extends a shouldered probe 174,182 extends. The probe is capable of axial translation within tubular body via axial translation of indicator tab 184. The shouldered probe is not retracted by a spring, and does not have radial translation capability relative to the first opening.
U.S. Pat. No. 5,013,318 (“Spranza”) also discloses a measuring device for measuring the diameter of a bone. The device comprises a tube having a first opening from which whiskers 1 extend. The whiskers open by activation of knob 6. The whiskers can not be retracted back into the body, and so do not have axial translation capability relative to the first opening.
In sum, each of the bone gages discussed above are capable of providing essentially only line-of-sight measurement, and none provide a gripping means which can be both axially and radially translated from the opening of the body having the measuring scale.
X-rays, CT-imaging, and fluoroscope can also be used to measure distances between sites within the body. These methods require more time because the pictures need to be obtained and then measured either during or prior to the surgery. The equipment is also cumbersome.
It would therefore be desirable to provide an enhanced device for measuring the distance between two points within a surgical site having none of the disadvantages described above.